1. Field Of The Invention
The present invention concerns a method and device for oxygenating and pumping blood circulated extra-corporeally in cardiovascular assistance.
During extra-corporeal circulation, in cardiovascular assistance, the blood must undergo those functions which are normally performed by the heart and lungs: it must be oxygenated and pumped. Such functions are at present effected separately by oxygenators and pumps, connected to the patient's circulation system to form a circuit in which may be included a blood collector tank, a blood filter and a temperature regulating device.
2. Description Of The Prior Art
The fluid-separation oxygenators used at present, which have in many places supplanted the old "bubble" oxygenators in which the oxygen was scrubbed directly into the blood, keep the blood separated from the oxygen by a surface interface constituted by, for example, a semipermeable membrane. This membrane is permeable only to gases and therefore permits the oxygen to pass through and replace the carbon dioxide present in the blood, which is eliminated through the membrane. Such membranes are usually tube-shaped, but can also be in other forms, better specified in what follows. Oxygenators are known both where the blood circulates in the spaces enclosed by the membrane while the oxygenating fluid flows outside, between the membrane and the walls of the oxygenator, and those where the blood circulates outside and the oxygen inside the space enclosed by the membrane. The pumps used are almost exclusively of the peristaltic or "roller" type; such pumps can be of a type where the blood is pumped with constant flow or with a pulsed flow. It has been found that, compared to continuous flow, pulsed flow has many advantages for the patient; in particular metabolism and various organ function are improved: the present tendency is therefore to use a pump which gives a pulsed blood flow.
The problems which arise with such apparatus are several; those of a more bio-medical character are caused essentially by the circulation of the blood in an artificial environment and by the volume of the apparatus to be filled with the blood to be circulated.
To avoid possible embolism, all the circuit of the blood from the tank to the patient must avoid blood-air contact; in particular, the blood must occupy all the available volume, both of the apparatus and in the tubes which connect it with the patient. This creates two main problems: first, by increasing the extra-corporeal circulation surface-area in contact with the blood, the chemical hemolysis caused by this contact is increased; secondly, the patient does not usually have sufficient blood to ensure circulation in his own system and in the apparatus, so blood, plasma or some other similar transfusion fluid has to be added to the patient's blood in order to make up the necessary volume. Since every fluid added to the blood causes so-called "transfusion shock" proportional to the volume of fluid added, it is obvious that the volume of added or "priming" fluid for extra-corporeal circulation must be kept to a minimum. As far as hemolysis damage is concerned, it is sufficient to remember that the free haemoglobin released by ruptured red corpuscles is deposited at kidney level and impedes in ever greater measure renal function and can cause serious damage leading even to death through renal failure.
Thus, an apparatus for extra-corporeal circulation is needed which reduces to a minimum chemical hemolysis and "transfusion shock".
An object of the present invention is to provide a method and device for extra-corporeal circulation of blood which solves the above problems, reducing the extra-corporeal circulation circuit and the "priming" volume necessary (it should be noted that where not otherwise indicated, hereinafter, the word "blood" means the patient's own blood plus any "priming" fluid or fluids).
This is accomplished by the unification of the blood pumping and oxygenation functions and the performance of both said functions simultaneously in one single device.